Any barrel that's not fit correctly to a reciver or not stress relieved after profiling, boring and rifling will bend as it heats up. Factory rifles are norious for this. Good quality match rifles will shoot to the same POI for 40 plus shots fired 30 seconds apart. Well, within 1/4 MOA anyway, 'cause barrel fouling and heat sometimes causes a few fps faster bullets that end up at the top of your group.

Lake City Arsenal's match ammo is fired for dozens of shots per test group. Group center doesn't change as their barrels heat up.